Cleaning method

ABSTRACT

IMPROVED METHOD OF CLEANING A FERROUS METAL SURFACE HAVING A HARDNESS DEPOSIT BY CONTACTING IT WITH AN AQUEOUS ALKALINE CLEANING SOLUTION CONTAINING ABOUT 0.1 TO 40 WEIGHT PERCENT OF AN AMMONIATED POLYCARBOXYLIC ACID COMPLEXING AGENT. THE IMPROVEMENT INVOLVES INCLUDING WITH THE SOLUTION IN AN AMOUNT OF FROM 0.0005 TO 0.1 WEIGHT PERCENT A CORROSION INHIBITING COMPOUND OF THE FORMULA:   R-CO-(O-CH2-CH(-OH)-CH2)A-NH-(CH2-CH2-NH)B-H   WHEREIN R IS AN ALKYL OR ALKENYL GROUP CONTAINING FROM 12 TO 18 CARBON ATOMS, A IS 1 OR 2 AND B IS 1-5.

United States Patent 3,668,009 CLEANING METHOD Fred Norman Teumac, South Bend, Ind, and Lester W. Harriman, Angleton, Tex., assignors to The Dow Chemical Company, Midland, Mich. No Drawing. Filed Apr. 13, 1970, Ser. No. 28,079 Int. Cl. (323g 1/16; B08b 3/08 U.S. Cl. 134-2 7 Claims ABSTRACT OF THE DISCLOSURE Improved method of cleaning a ferrous metal surface having a hardness deposit by contacting it with an aqueous alkaline cleaning solution containing about 0.1 to 40 weight percent of an ammoniated polycarboxylic acid complexing agent. The improvement involves including with the solution in an amount of from 0.0005 to 0.1 weight percent a corrosion inhibiting compound of the formula:

i f H iH H R- OC-CC-NCH CH N n H H/. 2- a A. wherein R is an alkyl or alkenyl group containing from 12 to 18 carbon atoms, a is l or 2 and b is 1-5.

The use of aqueous alkaline solutions of ammoniated polycarboxylic acid complexing agents for the cleaning of closed ferrous metal systems, e.g. steam boilers, is known. Among the complexiug agents which are useful in such a process are the mono or polysubstituted ammonium salts of ethylenediamine tetraacetic acid, diethylenetriaminepentacetic acid, nitrilotriacetic acid and citric acid.

The cleaning operation is normally carried out at elevated temperatures, i.e. 90 to 400 F. and preferably at about 300 F., thus making the use of a corrosion inhibitor desirable.

It is an object of the present invention to provide a method for inhibiting corrosion in the above-described cleaning operation.

An additional object is to provide such a method which employs inhibitors which are stable to decomposition at temperatures of up to about 400 F. and above.

An additional object is to provide a method of inhibiting corrosion which does not interfere with the removal of hardness scale from the ferrous metal surface being cleaned.

The invention is based upon the discovery that an aqueous alkaline solution of an ammoniated polycarboxylic acid complexing agent is effectively inhibited against attack on a ferrous metal surface at temperatures of up to about 400 F. by incorporating into the solution from about 0.0005 to about 0.1 percent by weight an inhibitor compound having the formula:

0 atlaatilsrmlofilarfi H H H/ n A In the above formula R is alkyl or alkenyl containing from 12 to 18 carbon atoms, a is l or 2 and b is 1-5.

In carrying out cleaning with the present inhibited cleaning solution, the solution is adjusted to a preselected alkaline pH normally in the range of from about 7.3 to 9.3 and the system to be cleaned is filled or otherwise contacted with the cleaning solution. The solution is then heated to a temperature of at least about 90 F. and preferably to a temperature of from 250 to 300 Temperatures as high as about 400 F. may be used. The hot cleaning solution is then maintained in contact with the ferrous metal surface for the requisite period of time 3,608,009 Patented June 6, 1972 when epichlorohydrin is reacted and:

H on 0 C when diglycidyl ether is employed.

After preparation of the monoepoxyester any excess epichlorohydrin or diglycidyl ether is removed by distillation, extraction or other means to a residual level of less than 5 percent and the ester reacted with an ethylene polyamine of the formula:

where b is an integer from 1 to 5. This process is more fully described in US. Pat. 3,467,684.

The corrosion inhibtors are viscous liquids which can be dispersed in water or in the concentrated cleaning solution. The inhibitor is dispersed in an amount sufficent to provide from 0.0005 to 0.1 weight percent of the final solution with 0.001 to 0.005 weight percent being the preferred concentration range.

The inhibitors are effective when used alone. It has been discovered that a strong synergistic action is demonstrated when certain sulfur containing compounds, i.e. thioethylamine, sodium mercaptobenzthiazole, bisethylamine bisulfide or thiazolidine, are added to the inhibited cleaning solution. These compounds are normally employed in an amount sufiicient to provide from 0.01 to 0.1 weight precent of the solution.

The invention is further illustrated by the following examples:

EXAMPLE I Inhibitor compounds were prepared as described above from the reactants set out in Table I. The usefulness of each inhibitor was determined by placing two polished, mild steel, 1" x 3" x A coupons along with a mill scaled (about .65 gm. Fe O coupon in a beaker containing a 3.8% solution of ammoniated EDTA containing the amount of inhibitor indicated. The beakers were placed in a pressure vessel and heated to 250 F. for 16 hours. At the end of the heating period the coupons, which were weighed before being placed in the beaker, were reweighed and the corrosion rate determined by the Weight loss. A control specimen was used with no inhibitor present upon which corrosion rates were determined intermittently during the 16 hour period. After the testing period all of the coupons were clean with no evidence of black deposits being observed.

Table I sets out the inhibitor, its concentration and the corrosion rate for each of 18 runs.

7 8 7. The process of claim 6 wherein the sulfur containing 3,072,502 1/1963 Alfa rio 1343 compound is added in an amount sufiicient to provide 3,248,269 4/1966 Bell 13,4 2;X

from 0.01 to 0.1 weight percent of the solution. 3,447,965 6/1969 Teumac 13 4,2

References Cited 5 MORRIS o. WOLK, Primary Examiner P J- T- Assistant Examiner 3,490,741 1/1970 Teumac et a1. 134-41 X U.'S. Cl. X.R. 3,467,684 9/1969 Lane 260-404.5 1343, 41 

